1. Field of the Invention
The present invention relates to improved method and apparatus for supporting pipe being laid in a body of water from a floating vessel.
2. Description of the Prior Art
In laying pipe on the floor of a body of water from a floating vessel in the conventional manner, a support structure or stinger is employed which extends outwardly from the vessel into the water to support the pipe. Failure to provide such a support structure may result in the weight of the pipe developing large stresses that can buckle or rupture the pipe. The problem of proper pipe support is compounded significantly in deep water, in heavy seas or with large diameter pipe, requiring the use of substantially larger stingers.
These outwardly extending structures present severe problems in heavy seas or adverse weather conditions. Because of the size of the stinger, environmental forces acting on it create tremendous bending moments at the hinge, frequently leading to hinge failures. Accordingly, stingers are normally detachably connected to the vessel so that they can be separated from the vessel during heavy seas or other adverse weather conditions.
Disconnection of the stinger from the vessel during heavy seas is, however, also a complex task and poses the possibility of damage to either the vessel or stinger. When these relatively massive stingers are detached and left to float free, they are a hazard to navigation and may damage the lay barge or a passing vessel. Further, reconnection of the floating stinger to the vessel must be delayed until the adverse weather subsides. Even then, however, it is a complex operation and often results in damage to the stinger, the vessel or both due to the relative motion therebetween.
A system has been proposed to raise the stinger out of the water at the onset of severe weather and to lower it into the operating position after the adverse weather subsides. Such a system, however, results in an elongated, massive cantilever beam extending off one end of the vessel. Even in the upraised position the stinger thus may be subject to significant environmental forces, leading to the development of large moments at the hinge which may damage the stinger and render it useless for continued operation.
Thus, the necessity of detaching and reconnecting or otherwise protecting the stinger during severe weather conditions poses serious problems.